Communication equipments such as cellular phones and smart phones are mounted with a system capable of communicating information using a flat coil antenna, such as NFC (near field (radio) communication) and payment system. In these communication equipments, the antenna is arranged close to a member including a metal, such as a circuit board and a battery, so that there tends to occur such a fear that the communication equipments are considerably deteriorated in communication sensitivity. For this reason, in order to increase the communication sensitivity, there has been proposed such an arrangement that a ferrite sintered sheet is disposed between the antenna and the member including a metal.
In these systems, in order to enhance the communication sensitivity, there has been proposed such a technology that a magnetic permeability of the ferrite sintered sheet is controlled by adding CoO to Ni—Zn—Cu ferrite (Patent Literatures 1 and 2).
On the other hand, in the application field of inductor, there has been proposed a method of obtaining a high-density inductor that is excellent in temperature characteristics of magnetic permeability by adding SnO2, Co oxide and Bi oxide thereto (Patent Literature 3). In addition, there has been proposed a method of controlling diffusion of Ag into ferrite by adjusting contents of S and Cl in the ferrite in respective predetermined ranges (Patent Literature 4). Furthermore, it is known that ferrite comprising SnO2 is used in an inductor (Patent Literature 5).